Spacewar! is a space combatvideo game developed in 1962 by Steve Russell, in collaboration with Martin Graetz and Wayne Wiitanen, and programmed by Russell with assistance from others including Bob Saunders and Steve Piner. It was written for the newly installed DECPDP-1 at the Massachusetts Institute of Technology. After its initial creation, Spacewar was expanded further by other students and employees of universities in the area, including Dan Edwards and Peter Samson. It was also spread to many of the few dozen, primarily academic, installations of the PDP-1 computer, making Spacewar the first known video game to be played at multiple computer installations.

The game features two spaceships, "the needle" and "the wedge", engaged in a dogfight while maneuvering in the gravity well of a star. Both ships are controlled by human players. Each ship has limited fuel for maneuvering and a limited number of torpedoes, and the ships follow Newtonian physics, remaining in motion even when the player is not accelerating. Flying near the star to provide a gravity assist was a common tactic. Ships are destroyed when hit by a torpedo or colliding with the star. At any time, the player can engage a hyperspace feature to move to a new, random location on the screen, though each use has an increasing chance of destroying the ship instead. The game was initially controlled with switches on the PDP-1, though Alan Kotok and Bob Saunders built an early gamepad to reduce the difficulty and awkwardness of controlling the game.

Spacewar is one of the most important and influential games in the early history of video games. It was extremely popular in the small programming community in the 1960s and was widely ported to other computer systems at the time. It has also been recreated in more modern programming languages for PDP-1 emulators. It directly inspired many other electronic games, such as the first commercial arcade games, Galaxy Game and Computer Space (1971), and later games such as Asteroids (1979). In 2007, Spacewar was named to a list of the ten most important video games of all time, which formed the start of the game canon at the Library of Congress.

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Steve Russell, designer and main programmer of the initial version of Spacewar, in 2007

During the 1950s, various computer games were created in the context of academic computer and programming research and for demonstrations of computing power, especially after the introduction later in the decade of smaller and faster computers on which programs could be created and run in real time as opposed to being executed in batches. A few programs, however, while used to showcase the power of the computer they ran on were also intended as entertainment products; these were generally created by undergraduate and graduate students and university employees, such as at the Massachusetts Institute of Technology (MIT) where they were allowed on occasion to develop programs for the TX-0 experimental computer.[1] These interactive graphical games were created by a community of programmers, many of them students and university employees affiliated with the Tech Model Railroad Club (TMRC) led by Alan Kotok, Peter Samson, and Bob Saunders. The games included Tic-Tac-Toe, which used a light pen to play a simple game of noughts and crosses against the computer, and Mouse in the Maze, which used a light pen to set up a maze of walls for a virtual mouse to traverse.[1][2][3]

In the fall of 1961, a Digital Equipment Corporation (DEC) PDP-1minicomputer was installed in the "kludge room" of the MIT Electrical Engineering Department to complement the older TX-0, and even before its arrival a group of students and university employees had been brainstorming ideas for programs that would demonstrate the new computer's capabilities in a compelling way. Three of them—Steve Russell, then an employee at Harvard University and a former research assistant at MIT; Martin Graetz, a research assistant and former student at MIT; and Wayne Wiitanen, a research assistant at Harvard and former employee and student at MIT—referring to their collaboration as the "Hingham Institute" as Graetz and Wiitanen were living in a tenement building on Hingham Street in Cambridge, Massachusetts, came up with the idea for Spacewar.[2][4] "We had this brand new PDP-1", Steve Russell told Rolling Stone in a 1972 interview. "Marvin Minsky [sic] had built some little pattern-generating programs which made interesting patterns like a kaleidoscope. Not a very good demonstration. Here was this display that could do all sorts of good things! So we started talking about it, figuring what would be interesting displays. We decided that probably you could make a two-dimensional maneuvering sort of thing, and decided that naturally the obvious thing to do was spaceships."[2][5]

The gameplay of Spacewar involves two monochrome spaceships called "the needle" and "the wedge", each controlled by a player, attempting to shoot one another while maneuvering on a two-dimensional plane in the gravity well of a star, set against the backdrop of a starfield.[2][4] The ships fire torpedoes which are not affected by the gravitational pull of the star. The ships have a limited number of torpedoes and a limited supply of fuel, which is used when the player fires his thrusters.[6] Torpedoes are fired one at a time by flipping a toggle switch on the computer or pressing a button on the control pad, and there is a cooldown period between launches. The ships follow Newtonian physics, remaining in motion even when the player is not accelerating, though the ships can rotate at a constant rate without inertia.[2]

Each player controls one of the ships and must attempt to shoot down the other ship while avoiding a collision with the star. Flying near the star can provide a gravity assist to the player at the risk of misjudging the trajectory and falling into the star. If a ship moves past one edge of the screen, it reappears on the other side in a wraparound effect. A hyperspace feature, or "panic button", can be used as a last-ditch means to evade enemy torpedoes by moving the player's ship to another location on the screen after disappearing for a few seconds, but the reentry from hyperspace occurs at a random location, and in some versions there is an increasing probability of the ship exploding with each use.[6]

Player controls include clockwise and counterclockwise rotation, forward thrust, firing torpedoes, and hyperspace.[6] Initially these were controlled using the front-panel test switches on the PDP-1 minicomputer, with four switches for each player, but these proved to be awkward to use and wore out quickly under normal gameplay, as well as causing players to accidentally flip the computer's control and power switches. The location of the switches also left one player off to one side of the CRT display due to the limited space in front of the computer, which left them at a disadvantage.[2] To alleviate these problems, Kotok and Saunders created a detached control device, essentially an early gamepad.[7][8] The gamepad had a switch for turning left or right, another for forward thrust or hyperspace, and a torpedo launch button. The button was silent so that the opposing player would not have a warning that the player was attempting to fire a torpedo during a cooldown period.[2]

In the fall of 1961, while discussing ideas for a program for the PDP-1, Russell had finished reading the Lensman series by E. E. "Doc" Smith and thought the stories would make a good basis for the program. "His heroes had a strong tendency to get pursued by the villain across the galaxy and have to invent their way out of their problem while they were being pursued. That sort of action was the thing that suggested Spacewar. He had some very glowing descriptions of spaceship encounters and space fleet maneuvers."[5] Other influences cited by fellow programmer Martin Graetz include E.E. Smith's Skylark novels and Japanese pulp fiction tokusatsumovies.[9]

For the first few months after its installation, the PDP-1 programming community at MIT focused on simpler programs to work out how to create software for the computer.[2] The community had heard of the Spacewar concept, however, and understood that Russell would spearhead the development of it. When members of the community began to feel the time was right to start work on the game, Russell, nicknamed "Slug" because of his tendency to procrastinate, began providing various excuses as to why he could not start programming the game.[2][10] One of these was the lack of a trigonometric function routine needed to calculate the trajectories of the spacecraft. This prompted Alan Kotok of TMRC to call DEC, who informed him that they had such a routine already written. Kotok drove to DEC to pick up a tape containing the code, slammed it down in front of Russell, and asked what other excuses he had. Russell, later explaining that "I looked around and I didn't find an excuse, so I had to settle down and do some figuring," started writing the code in December 1961.[2][10] The game was developed to meet three precepts Russell, Graetz, and Wiitanen had developed for creating a program that functioned equally well as an entertainment experience for the players and as a demonstration for spectators: to use as much of the computer's resources as possible, to be consistently interesting and therefore have every run be different, and to be entertaining and therefore a game.[2][11] It took Russell, with assistance from the other programmers—including Bob Saunders and Steve Piner (but not Wiitanen, who had been called up by the United States Army Reserve)—about 200 man-hours to write the first version of Spacewar, or around six weeks to develop the basic game.[2][10][12]

Excerpt from the Expensive Planetarium star charts

Russell had a program with a movable dot by January 1962, and an early operational game with rotatable spaceships by February.[2] The two spaceships were designed to evoke the curvy spaceship from Buck Rogers stories and the PGM-11 Redstone rocket.[4] That early version also contained a randomly generated background star field, initially added by Russell because a blank background made it difficult to tell the relative motion of the two spaceships at slow speeds.[2] The programming community in the area, including the Hingham Institute and the TMRC, had developed what was later termed the "hacker ethic", whereby all programs were freely shared and modified by other programmers in a collaborative environment without concern for ownership or copyright, which led to a group effort to elaborate on Russell's initial Spacewar game.[4][12] Consequently, since the inaccuracy and lack of realism in the star field annoyed TMRC member Peter Samson, he wrote a program based on real star charts that scrolled slowly through the night sky, including every star in a band between 22.5° N and 22.5° S down to the fifth magnitude, displayed at their relative brightness. The program was called "Expensive Planetarium"—referring to the high price of the PDP-1 computer compared to an analog planetarium, as part of the series of "expensive" programs like Expensive Typewriter—and was quickly incorporated into the game in March by Russell, who served as the collator of the primary version of the game.[2][4][7]

The initial version of the game also did not include the central star gravity well or the hyperspace feature; they were written by MIT graduate student and TMRC member Dan Edwards and Graetz respectively to add elements of a strategy to what initially was a shooter game of pure reflexes. The initial version of the hyperspace function was limited to three jumps, but carried no risk save possibly re-entering the game in a dangerous position; later versions removed the limit but added the increasing risk of destroying the ship instead of moving it. Additionally, during this development period, Kotok and Saunders created the gamepads for the game.[2] The game was a multiplayer-only game because the computer had no resources left over to handle controlling the other ship.[7][13] Similarly, other proposed additions to the game such as a more refined explosion display upon the destruction of a spaceship and having the torpedoes also be affected by gravity had to be abandoned as there were not enough computer resources to handle them while smoothly running the game.[2] With the added features and changes, Spacewar was essentially complete by late April 1962, and Russell and the other programmers shifted focus from developing the game to preparing to show it off to others such as at the MIT Science Open House in May.[2][14] The group added a time limit, as well as a larger, second screen for viewers at the demonstration, and that same month Graetz presented a paper about the game, "SPACEWAR! Real-Time Capability of the PDP-1", at the first meeting of the Digital Equipment Computer Users' Society.[2] The demonstration was a success, and the game proved very popular at MIT; the laboratory that hosted the PDP-1 soon banned play except during lunch and after working hours.[2][15] Visitors such as Frederik Pohl enjoyed playing the "lovely game"; the editor of Galaxy Science Fiction wrote that MIT was "borrowing from the science-fiction magazines", with players able to pretend being Skylark characters.[16]

Beginning in the summer of 1962 and continuing over the next few years, members of the PDP-1 programming community at MIT, including Russell and the other Hingham Institute members, began to spread out to other schools and employers such as Stanford University and DEC, and as they did they spread the game to other universities and institutions with a PDP-1 computer.[2][4][7] As a result, Spacewar was perhaps the first video game to be available outside a single research institute.[17] Over the next decade, programmers at these other institutions began coding their own variants, including features such as allowing more ships and players at once, replacing the hyperspace feature with a cloaking device, space mines, and even a first-person perspective version played on two screens that simulates each pilot's view out of the cockpit.[5][6] Some of these Spacewar installations also replicated Kotok and Saunders' gamepad.[18] According to a second-hand account heard by Russell while working at DEC, Spacewar was reportedly used as a smoke test by DEC technicians on new PDP-1 systems before shipping because it was the only available program that exercised every aspect of the hardware.[12][18] Although the game was widespread for the era, it was still very limited in its direct reach: the PDP-1 was priced at US$120,000 and only 55 were ever sold, most without a monitor and many of the remainder to secure military locations or research labs with no free computer time, which prevented the original Spacewar from reaching beyond a narrow, academic audience.[4][7][18] Though some later DEC models, such as the PDP-6, came with Spacewarpre-loaded, the audience for the game remained very limited; the PDP-6, for example, sold only 23 units.[8][19]

Spacewar was extremely popular in the small programming community in the 1960s and was widely recreated on other minicomputer and mainframe computers of the time before migrating to early microcomputer systems in the 1970s.[4] Early computer scientistAlan Kay noted in 1972 that "the game of Spacewar blossoms spontaneously wherever there is a graphics display connected to a computer," and Graetz recalled in 1981 that as the game initially spread it could be found on "just about any research computer that had a programmable CRT".[2][5] The majority of this spread took place several years after the initial development of the game; while there are early anecdotes of players and game variants at a handful of locations, primarily near MIT and Stanford, it was only after 1967 that computers hooked up to monitors or terminals capable of playing Spacewar began to proliferate, allowing the game to reach a wider audience and influence later video game designers—by 1971, it is estimated that there were over 1000 computers with monitors, rather than a few dozen.[18] It is around this time that the majority of the game variants were created for various computer systems, such as later PDP systems, and in 1972 the game was well-known enough in the programming community that Rolling Stone sponsored the "SpaceWar! Olympics", possibly the first video game tournament.[5][18]

In the early 1970s, Spacewar migrated from large computer systems to a commercial setting as it formed the basis for the first two coin-operated video games. While playing Spacewar at Stanford sometime between 1966 and 1969, college student Hugh Tuck remarked that a coin-operated version of the game would be very successful. While the high price of a minicomputer prevented such a game from being feasible then, in 1971 Tuck and Bill Pitts created a prototype coin-operated computer game, Galaxy Game, with a US$20,000 PDP-11. Around the same time, a second prototype coin-operated game based on Spacewar, Computer Space, was developed by Nolan Bushnell and Ted Dabney, which would become the first commercially sold arcade video game and the first widely available video game of any kind.[20] Though Tuck felt that Computer Space was a poor imitation of Spacewar and his game a superior adaptation, many players believed both of the games to be upgraded variants of Spacewar.[11]

In addition to Galaxy Game and Computer Space, numerous other games have been directly inspired by Spacewar.[26] These include Orbitwar (1974, PLATO network computers), Space Wars (1977, arcade), and Space War (1978, Atari 2600).[27][28] Additionally, in Asteroids (1979), designer Ed Logg used elements from Spacewar, namely the hyperspace button and the shape of the player's ship.[29] Products as late as the 1990 computer game Star Control drew direct inspiration from Spacewar.[18] Russell has been quoted as saying that the aspect of the game that he was most pleased with was the number of other programmers it inspired to write their own games without feeling restricted to using Russell's own code or design.[15]

On March 12, 2007, The New York Times reported that Spacewar was named to a list of the ten most important video games of all time, the so-called game canon, which were proposed to be archived in the Library of Congress.[30] The Library of Congress took up this video game preservation proposal, and began with the games from this list.[31][32]

1.
Computing platform
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Computing platform means in general sense, where any piece of software is executed. It may be the hardware or the system, even a web browser or other application. The term computing platform can refer to different abstraction levels, including a hardware architecture, an operating system. In total it can be said to be the stage on which programs can run. For example, an OS may be a platform that abstracts the underlying differences in hardware, platforms may also include, Hardware alone, in the case of small embedded systems. Embedded systems can access hardware directly, without an OS, this is referred to as running on bare metal, a browser in the case of web-based software. The browser itself runs on a platform, but this is not relevant to software running within the browser. An application, such as a spreadsheet or word processor, which hosts software written in a scripting language. This can be extended to writing fully-fledged applications with the Microsoft Office suite as a platform, software frameworks that provide ready-made functionality. Cloud computing and Platform as a Service, the social networking sites Twitter and facebook are also considered development platforms. A virtual machine such as the Java virtual machine, applications are compiled into a format similar to machine code, known as bytecode, which is then executed by the VM. A virtualized version of a system, including virtualized hardware, OS, software. These allow, for instance, a typical Windows program to run on what is physically a Mac, some architectures have multiple layers, with each layer acting as a platform to the one above it. In general, a component only has to be adapted to the layer immediately beneath it, however, the JVM, the layer beneath the application, does have to be built separately for each OS

2.
PDP-1
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The PDP-1 was the first computer in Digital Equipment Corporations PDP series and was first produced in 1959. It is famous for being the computer most important in the creation of culture at MIT, BBN. The PDP-1 was also the hardware for playing historys first game on a minicomputer. The PDP-1 used an 18-bit word size and had 4096 words as standard main memory, signed numbers were represented in ones complement. The PDP-1 had computing power roughly equivalent to a 1996 pocket organizer, the PDP-1 used 2,700 transistors and 3,000 diodes. It was built mostly of DEC 1000-series System Building Blocks, using micro-alloy and micro-alloy diffused transistors with a rated switching speed of 5 MHz, the System Building Blocks were packaged into several 19-inch racks. The racks were themselves packaged into a large mainframe case, with a hexagonal control panel containing switches. Above the control panel was the systems standard input/output solution, a tape reader and writer. The design of the PDP-1 was based on the pioneering TX-0 computer, designed, benjamin Gurley was the lead engineer on the project. After building prototype models in December 1959, DEC delivered the first PDP-1 to Bolt, Beranek and Newman in November 1960, and it was formally accepted the next April. In 1961, DEC donated the engineering prototype PDP-1 to MIT, where it was placed in the next to its ancestor, the TX-0 computer. In this setting, the PDP-1 quickly replaced the TX-0 as the favorite machine among the hacker culture. Perhaps best known among these is one of the first computerized video games, but among the list are the first text editor, word processor, interactive debugger, the first credible computer chess program, and some of the earliest computerized music. The PDP-1 sold in form for US$120,000. BBNs system was followed by orders from Lawrence Livermore and Atomic Energy of Canada. All of these machines were still being used in 1970. MITs example was donated to The Computer Museum, Boston, on paper tape was still tucked into the case. AECLs computer was sent to Science North, but was later scrapped, the PDP-1 used punched paper tape as its primary storage medium

3.
North America
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North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be considered a subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the southeast by South America and the Caribbean Sea. North America covers an area of about 24,709,000 square kilometers, about 16. 5% of the land area. North America is the third largest continent by area, following Asia and Africa, and the fourth by population after Asia, Africa, and Europe. In 2013, its population was estimated at nearly 565 million people in 23 independent states, or about 7. 5% of the worlds population, North America was reached by its first human populations during the last glacial period, via crossing the Bering land bridge. The so-called Paleo-Indian period is taken to have lasted until about 10,000 years ago, the Classic stage spans roughly the 6th to 13th centuries. The Pre-Columbian era ended with the migrations and the arrival of European settlers during the Age of Discovery. Present-day cultural and ethnic patterns reflect different kind of interactions between European colonists, indigenous peoples, African slaves and their descendants, European influences are strongest in the northern parts of the continent while indigenous and African influences are relatively stronger in the south. Because of the history of colonialism, most North Americans speak English, Spanish or French, the Americas are usually accepted as having been named after the Italian explorer Amerigo Vespucci by the German cartographers Martin Waldseemüller and Matthias Ringmann. Vespucci, who explored South America between 1497 and 1502, was the first European to suggest that the Americas were not the East Indies, but a different landmass previously unknown by Europeans. In 1507, Waldseemüller produced a map, in which he placed the word America on the continent of South America. He explained the rationale for the name in the accompanying book Cosmographiae Introductio, for Waldseemüller, no one should object to the naming of the land after its discoverer. He used the Latinized version of Vespuccis name, but in its feminine form America, following the examples of Europa, Asia and Africa. Later, other mapmakers extended the name America to the continent, In 1538. Some argue that the convention is to use the surname for naming discoveries except in the case of royalty, a minutely explored belief that has been advanced is that America was named for a Spanish sailor bearing the ancient Visigothic name of Amairick. Another is that the name is rooted in a Native American language, the term North America maintains various definitions in accordance with location and context. In Canadian English, North America may be used to refer to the United States, alternatively, usage sometimes includes Greenland and Mexico, as well as offshore islands

4.
Space flight simulation game
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A space flight simulation game is a genre of flight simulator video games that lets players experience space flight. Examples of true simulators which aim at piloting a craft in a manner that conforms with the laws of nature include Orbiter, Kerbal Space Program. Space flight games and simulators, at one time popular, had for most of the new millennium been considered a dead genre. Some more recent games, most notably Star Citizen, Elite, Dangerous, others focus on gameplay rather than simulating space flight in all its facets. The realism of the games is limited to what the game designer deems to be appropriate for the gameplay. Most of the pseudo simulators feature faster than light travel, realistic space simulators seek to represent a vessels behaviour under the influence of the Laws of Physics. As such, the player concentrates on following checklists or planning tasks. Piloting is generally limited to dockings, landings or orbital maneuvers, the reward for the player is on mastering real or realistic spacecraft, celestial mechanics and astronautics. Classical games with this approach include Space Shuttle, A Journey into Space, Rendezvous, A Space Shuttle Simulation, The Halley Project, Shuttle and Microsoft Space Simulator. If the definition is expanded to include making and planning, then Buzz Aldrins Race Into Space is also notable for historical accuracy. On this game the player takes the role of Administrator of NASA or Head of the Soviet Space Program with the goal of being the first side to conduct a successful manned moon landing. Most recently Orbiter and Space Shuttle Mission 2007 provide more elaborate simulations, with realistic 3D virtual cockpits, Kerbal Space Program can be considered a space simulator, even though it portrays an imaginary universe with tweaked physics, masses and distances to enhance gameplay. Nevertheless, the physics and rocket design principles are more realistic than in the space combat or trading subgenres. The game Lunar Flight simulates flying around the surface in a craft resembling the Apollo Lunar Module. Most games in the space combat genre feature futuristic scenarios involving space flight, the prominent Wing Commander, Tachyon, The Fringe, X-Wing and Freespace series all use this approach. Exceptions include the first Independence War and the Star Trek, Bridge Commander series and it should be noted that I-War also features Newtonian style physics for the behaviour of the space craft, but not orbital mechanics. Space combat games tend to be mission-based, as opposed to the more open-ended nature of space trading, the ship the player controls is generally larger than that in pure space combat simulator. Notable examples of the genre include Elite, Wing Commander, Privateer, in some instances, plot plays only a limited role and only a loose narrative framework tends to be provided

5.
Video game
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A video game is an electronic game that involves interaction with a user interface to generate visual feedback on a video device such as a TV screen or computer monitor. The word video in video game referred to a raster display device. Some theorists categorize video games as an art form, but this designation is controversial, the electronic systems used to play video games are known as platforms, examples of these are personal computers and video game consoles. These platforms range from large mainframe computers to small handheld computing devices, the input device used for games, the game controller, varies across platforms. Common controllers include gamepads, joysticks, mouse devices, keyboards, the touchscreens of mobile devices, and buttons, or even, with the Kinect sensor, a persons hands and body. Players typically view the game on a screen or television or computer monitor, or sometimes on virtual reality head-mounted display goggles. There are often game sound effects, music and, in the 2010s, some games in the 2000s include haptic, vibration-creating effects, force feedback peripherals and virtual reality headsets. In the 2010s, the game industry is of increasing commercial importance, with growth driven particularly by the emerging Asian markets and mobile games. As of 2015, video games generated sales of USD74 billion annually worldwide, early games used interactive electronic devices with various display formats. The earliest example is from 1947—a Cathode ray tube Amusement Device was filed for a patent on 25 January 1947, by Thomas T. Goldsmith Jr. and Estle Ray Mann, and issued on 14 December 1948, as U. S. Written by MIT students Martin Graetz, Steve Russell, and Wayne Wiitanens on a DEC PDP-1 computer in 1961, and the hit ping pong-style Pong, used the DEC PDP-1s vector display to have two spaceships battle each other. In 1971, Computer Space, created by Nolan Bushnell and Ted Dabney, was the first commercially sold and it used a black-and-white television for its display, and the computer system was made of 74 series TTL chips. The game was featured in the 1973 science fiction film Soylent Green, Computer Space was followed in 1972 by the Magnavox Odyssey, the first home console. Modeled after a late 1960s prototype console developed by Ralph H. Baer called the Brown Box and these were followed by two versions of Ataris Pong, an arcade version in 1972 and a home version in 1975 that dramatically increased video game popularity. The commercial success of Pong led numerous other companies to develop Pong clones and their own systems, the game inspired arcade machines to become prevalent in mainstream locations such as shopping malls, traditional storefronts, restaurants, and convenience stores. The game also became the subject of articles and stories on television and in newspapers and magazines. Space Invaders was soon licensed for the Atari VCS, becoming the first killer app, the term platform refers to the specific combination of electronic components or computer hardware which, in conjunction with software, allows a video game to operate. The term system is commonly used

6.
Digital Equipment Corporation
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Digital Equipment Corporation, also known as DEC and using the trademark Digital, was a major American company in the computer industry from the 1950s to the 1990s. DEC was a vendor of computer systems, including computers, software. Their PDP and successor VAX products were the most successful of all minicomputers in terms of sales, DEC was acquired in June 1998 by Compaq, in what was at that time the largest merger in the history of the computer industry. At the time, Compaq was focused on the market and had recently purchased several other large vendors. DEC was a major player overseas where Compaq had less presence, however, Compaq had little idea what to do with its acquisitions, and soon found itself in financial difficulty of its own. The company subsequently merged with Hewlett-Packard in May 2002, as of 2007 some of DECs product lines were still produced under the HP name. From 1957 until 1992, DECs headquarters were located in a wool mill in Maynard. DEC was acquired in June 1998 by Compaq, which merged with Hewlett-Packard in May 2002. Some parts of DEC, notably the business and the Hudson. Initially focusing on the end of the computer market allowed DEC to grow without its potential competitors making serious efforts to compete with them. Their PDP series of machines became popular in the 1960s, especially the PDP-8, looking to simplify and update their line, DEC replaced most of their smaller machines with the PDP-11 in 1970, eventually selling over 600,000 units and cementing DECs position in the industry. Originally designed as a follow-on to the PDP-11, DECs VAX-11 series was the first widely used 32-bit minicomputer and these systems were able to compete in many roles with larger mainframe computers, such as the IBM System/370. The VAX was a best-seller, with over 400,000 sold, at its peak, DEC was the second largest employer in Massachusetts, second only to the Massachusetts State Government. The rapid rise of the business microcomputer in the late 1980s, DECs last major attempt to find a space in the rapidly changing market was the DEC Alpha 64-bit RISC instruction set architecture. DEC initially started work on Alpha as a way to re-implement their VAX series, DEC was acquired in June 1998 by Compaq, in what was at that time the largest merger in the history of the computer industry. At the time, Compaq was focused on the market and had recently purchased several other large vendors. DEC was a major player overseas where Compaq had less presence, however, Compaq had little idea what to do with its acquisitions, and soon found itself in financial difficulty of its own. The company subsequently merged with Hewlett-Packard in May 2002, as of 2007 some of DECs product lines were still produced under the HP name

7.
Massachusetts Institute of Technology
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The Massachusetts Institute of Technology is a private research university in Cambridge, Massachusetts, often cited as one of the worlds most prestigious universities. Researchers worked on computers, radar, and inertial guidance during World War II, post-war defense research contributed to the rapid expansion of the faculty and campus under James Killian. The current 168-acre campus opened in 1916 and extends over 1 mile along the bank of the Charles River basin. The Institute is traditionally known for its research and education in the sciences and engineering, and more recently in biology, economics, linguistics. Air Force and 6 Fields Medalists have been affiliated with MIT, the school has a strong entrepreneurial culture, and the aggregated revenues of companies founded by MIT alumni would rank as the eleventh-largest economy in the world. In 1859, a proposal was submitted to the Massachusetts General Court to use newly filled lands in Back Bay, Boston for a Conservatory of Art and Science, but the proposal failed. A charter for the incorporation of the Massachusetts Institute of Technology, Rogers, a professor from the University of Virginia, wanted to establish an institution to address rapid scientific and technological advances. The Rogers Plan reflected the German research university model, emphasizing an independent faculty engaged in research, as well as instruction oriented around seminars, two days after the charter was issued, the first battle of the Civil War broke out. After a long delay through the war years, MITs first classes were held in the Mercantile Building in Boston in 1865, in 1863 under the same act, the Commonwealth of Massachusetts founded the Massachusetts Agricultural College, which developed as the University of Massachusetts Amherst. In 1866, the proceeds from sales went toward new buildings in the Back Bay. MIT was informally called Boston Tech, the institute adopted the European polytechnic university model and emphasized laboratory instruction from an early date. Despite chronic financial problems, the institute saw growth in the last two decades of the 19th century under President Francis Amasa Walker. Programs in electrical, chemical, marine, and sanitary engineering were introduced, new buildings were built, the curriculum drifted to a vocational emphasis, with less focus on theoretical science. The fledgling school still suffered from chronic financial shortages which diverted the attention of the MIT leadership, during these Boston Tech years, MIT faculty and alumni rebuffed Harvard University president Charles W. Eliots repeated attempts to merge MIT with Harvard Colleges Lawrence Scientific School. There would be at least six attempts to absorb MIT into Harvard, in its cramped Back Bay location, MIT could not afford to expand its overcrowded facilities, driving a desperate search for a new campus and funding. Eventually the MIT Corporation approved an agreement to merge with Harvard, over the vehement objections of MIT faculty, students. However, a 1917 decision by the Massachusetts Supreme Judicial Court effectively put an end to the merger scheme, the neoclassical New Technology campus was designed by William W. Bosworth and had been funded largely by anonymous donations from a mysterious Mr. Smith, starting in 1912. In January 1920, the donor was revealed to be the industrialist George Eastman of Rochester, New York, who had invented methods of production and processing

8.
Gravity well
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The Sun is very massive, relative to other bodies in the Solar System, so the corresponding gravity well that surrounds it appears deep and far-reaching. The gravity wells of asteroids and small moons, conversely, are depicted as very shallow. The deeper a gravity well is, the energy any space-bound climber must use to escape it. In astrophysics, a gravity well is specifically the potential field around a massive body. Other types of potential wells include electrical and magnetic potential wells, physical models of gravity wells are sometimes used to illustrate orbital mechanics. Gravity wells are frequently confused with embedding diagrams used in relativity theory. If G is the gravitational constant, the external gravitational potential of a spherically symmetric body of mass M is given by the formula. A plot of this function in two dimensions is shown in the figure, the potential function has a hyperbolic cross section, the sudden dip in the center is the origin of the name gravity well. A black hole would not have this closing dip due to its size being only determined by its event horizon, in a uniform gravitational field, the gravitational potential at a point is proportional to the height. As a result, an object constrained to move on the surface will have roughly the same equation of motion as an object moving in the potential field Φ itself, gravity wells constructed on this principle can be found in many science museums. There are several sources of inaccuracy in this model, The friction between the object and the surface has no analogue in vacuum and this effect can be reduced by using a rolling ball instead of a sliding block. The objects vertical motion contributes kinetic energy which has no analogue and this effect can be reduced by making the gravity well shallower. A rolling balls rotational kinetic energy has no analogue and this effect can be reduced by concentrating the balls mass near its center so that the moment of inertia is small compared to mr². A balls center of mass is not located on the surface but at a distance r. For balls of a size, this effect can be eliminated by constructing the surface so that the center of the ball, rather than the surface itself. Consider an idealized rubber sheet suspended in a gravitational field normal to the sheet. The mass density may be viewed as intrinsic to the sheet or as belonging to objects resting on top of the sheet. This equilibrium condition is identical in form to the gravitational Poisson equation ∇2 Φ = −4 π G ρ where Φ is the gravitational potential, in particular, the embedding diagram most commonly found in textbooks superficially resembles a gravity well

9.
Classical mechanics
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In physics, classical mechanics is one of the two major sub-fields of mechanics, along with quantum mechanics. Classical mechanics is concerned with the set of physical laws describing the motion of bodies under the influence of a system of forces. The study of the motion of bodies is an ancient one, making classical mechanics one of the oldest and largest subjects in science, engineering and technology. Classical mechanics describes the motion of objects, from projectiles to parts of machinery, as well as astronomical objects, such as spacecraft, planets, stars. Within classical mechanics are fields of study that describe the behavior of solids, liquids and gases, Classical mechanics also provides extremely accurate results as long as the domain of study is restricted to large objects and the speeds involved do not approach the speed of light. When both quantum and classical mechanics cannot apply, such as at the level with high speeds. Since these aspects of physics were developed long before the emergence of quantum physics and relativity, however, a number of modern sources do include relativistic mechanics, which in their view represents classical mechanics in its most developed and accurate form. Later, more abstract and general methods were developed, leading to reformulations of classical mechanics known as Lagrangian mechanics and these advances were largely made in the 18th and 19th centuries, and they extend substantially beyond Newtons work, particularly through their use of analytical mechanics. The following introduces the concepts of classical mechanics. For simplicity, it often models real-world objects as point particles, the motion of a point particle is characterized by a small number of parameters, its position, mass, and the forces applied to it. Each of these parameters is discussed in turn, in reality, the kind of objects that classical mechanics can describe always have a non-zero size. Objects with non-zero size have more complicated behavior than hypothetical point particles, because of the degrees of freedom. However, the results for point particles can be used to such objects by treating them as composite objects. The center of mass of a composite object behaves like a point particle, Classical mechanics uses common-sense notions of how matter and forces exist and interact. It assumes that matter and energy have definite, knowable attributes such as where an object is in space, non-relativistic mechanics also assumes that forces act instantaneously. The position of a point particle is defined with respect to a fixed reference point in space called the origin O, in space. A simple coordinate system might describe the position of a point P by means of a designated as r. In general, the point particle need not be stationary relative to O, such that r is a function of t, the time

10.
Gravity assist
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Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path. The assist is provided by the motion of the body as it pulls on the spacecraft. It was used by interplanetary probes from Mariner 10 onwards, including the two Voyager probes notable flybys of Jupiter and Saturn, a gravity assist around a planet changes a spacecrafts velocity by entering and leaving the gravitational field of a planet. The spacecrafts speed increases as it approaches the planet and decreases while escaping its gravitational pull, because the planet orbits the sun, the spacecraft is affected by this motion during the maneuver. To increase speed, the flies with the movement of the planet, to decrease speed. The sum of the energies of both bodies remains constant. A slingshot maneuver can therefore be used to change the spaceships trajectory, a close terrestrial analogy is provided by a tennis ball bouncing off the front of a moving train. Imagine standing on a platform, and throwing a ball at 30 km/h toward a train approaching at 50 km/h. The driver of the sees the ball approaching at 80 km/h. Because of the motion, however, that departure is at 130 km/h relative to the train platform. Translating this analogy into space, in the reference frame. After the slingshot occurs and the leaves the planet, it will still have a velocity of v. In the Sun reference frame, the planet has a velocity of v, and by using the Pythagorean Theorem. After the spaceship leaves the planet, it will have a velocity of v + v = 2v and this example is also one of many trajectories and gained speeds the spaceship can have. The linear momentum gained by the spaceship is equal in magnitude to that lost by the planet, so the spacecraft gains velocity, however, the planets enormous mass compared to the spacecraft makes the resulting change in its speed negligibly small. These effects on the planet are so slight that they can be ignored in the calculation, realistic portrayals of encounters in space require the consideration of three dimensions. The same principles apply, only adding the planets velocity to that of the spacecraft requires vector addition, due to the reversibility of orbits, gravitational slingshots can also be used to reduce the speed of a spacecraft. Both Mariner 10 and MESSENGER performed this maneuver to reach Mercury, if even more speed is needed than available from gravity assist alone, the most economical way to utilize a rocket burn is to do it near the periapsis

11.
Alan Kotok
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Alan Kotok was an American computer scientist known for his work at Digital Equipment Corporation and at the World Wide Web Consortium. Steven Levy, in his book Hackers, Heroes of the Computer Revolution, describes Kotok, Kotok was a precocious child who skipped two grades before college. Together with his teacher John McCarthy and other classmates, he was part of the team wrote the Kotok-McCarthy program which took part in the first chess match between computers. After leaving MIT, Kotok joined the computer manufacturer DEC, where he worked for over 30 years and he was the chief architect of the PDP-10 family of computers, and created the companys Internet Business Group, responsible for several forms of Web-based technology. Alan Kotok was born in 1941 in Philadelphia, Pennsylvania, and was raised as a child in Vineland. During his childhood, he played with tools in his fathers hardware store and he was a precocious child, skipping two grades at high school, and he matriculated at Massachusetts Institute of Technology aged 16. In 1977, at age 36, Kotok married Judith McCoy and they lived in Cambridge, Massachusetts and Cape May, New Jersey. The couple shared a love of 16th and 17th-century music and pipe organs and they had a daughter, Leah Kotok, and two stepchildren from Judiths prior marriage, Frederica and Daryl Beck. Kotok recorded a history at the Computer History Museum in 2004. He died at his home in Cambridge, apparently from an attack, on May 26,2006. At MIT, Kotok earned bachelors and masters degrees in electrical engineering and he was influenced by teachers such as Jack Dennis and John McCarthy and by his involvement in the student-organized Tech Model Railroad Club, which he joined soon after starting college in 1958. While a graduate student and member of TMRC, Dennis introduced his students to the TX-0 on loan to MIT indefinitely from Lincoln Laboratory, in the spring of 1959, McCarthy taught the first course in programming that MIT offered to freshmen. Outside classes, Kotok, David Gross, Peter Samson, Robert A. Saunders and Robert A. Wagner, all friends from TMRC, reserved time on the TX-0. They were able to use the TX-0 as a personal, single-user tool rather than a batch processing system, thanks to Dennis, faculty advisors and John McKenzie, in September 1961, Digital donated a PDP-1 to MIT. Although not a machine, and with a tiny 9K of memory. Dennis oversaw the PDP-1 lab, located next door to the TX-0, students from TMRC worked as support staff, programming the new computer. With classmates Elwyn Berlekamp, Michael Lieberman, Charles Niessen and Wagner, Kotok described their work in MIT Artificial Intelligence Project Memo 41 and in his bachelors thesis. By the time the group graduated in 1962, their program played chess comparable to an amateur with about 100 games experience on an IBM7090

12.
Gamepad
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A gamepad, is a type of game controller held in two hands, where the fingers are used to provide input. They are typically the main input device for video game consoles, gamepads generally feature a set of buttons handled with the right thumb and a direction controller handled with the left. The direction controller has traditionally been a four-way digital cross, there are programmable joysticks that can emulate keyboard input. Generally they have made to circumvent the lack of joystick support in some computer games. Initially used toggle switches built into the computer display to control the game. These switches were awkward and uncomfortable to use, so Alan Kotok and Bob Saunders built and this device has been called the earliest gamepad. The third generation of video games saw many changes. Nintendo developed a device for directional inputs, a D-pad with a cross design for their Donkey Kong handheld game. This design would be incorporated into their Game & Watch series, though developed because they were more compact than joysticks, and thus more appropriate for handheld games, game designers soon discovered that D-pads were more comfortable to use than joysticks. The original Sega Genesis control pad has three buttons, but a six-button pad was later released. The inclusion of six action buttons was influenced by the popularity of the Street Fighter arcade series, for most of the 1980s and early 1990s, analog joysticks were the predominant form of gaming controller for PCs, while console gaming controllers were mostly digital. This changed in 1996, when all three major consoles introduced an optional analog control, despite these changes, gamepads essentially continued to follow the template set by the NES controller. Gamepads failed to any soft of dominance outside of the home console market, though several PC gamepads have enjoyed popularity. In 1994 Logitech introduced the CyberMan, the first practical six degrees of freedom controller, but due to its price, poor build quality. Industry insiders blame the CyberMans high profile and costly failure for the gaming industrys lack of interest in developing 3D control over the several years. The Wii Remote is shaped like a remote control and contains tilt sensors and three-dimensional pointing which allows the system to understand all directions of movement. The controller is also multifunctional and includes a bay which can be used with different types of peripherals. An analog stick peripheral called Nunchuk also contains an accelerometer but unlike the Wii Remote, gamepads are also available for personal computers

13.
Early history of video games
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The history of video games spans a period of time between the invention of the first electronic games and today, covering a long period of invention and changes. Video gaming would not reach popularity until the 1970s and 1980s. Since then, video gaming has become a form of entertainment. Initially created as technology demonstrations, such as the Bertie the Brain and Nimrod computers in 1950 and 1951, a series of games, generally simulating real-world board games, were created at various research institutions to explore programming, human–computer interaction, and computer algorithms. These include OXO and Christopher Stracheys draughts program in 1952, the first software-based games to incorporate a CRT display, possibly the first video game created simply for entertainment was 1958s Tennis for Two, featuring moving graphics on an oscilloscope. Throughout the rest of the 1960s, digital computer games were created by increasingly numerous programmers, the term video game has evolved over the decades from a purely technical definition to a general concept defining a new class of interactive entertainment. Technically, for a product to be a game, there must be a video signal transmitted to a cathode ray tube that creates a rasterized image on a screen. From a technical standpoint, these would more properly be called games or computer games. Today, however, the video game has completely shed its purely technical definition. The ancestors to these include the cathode-ray tube amusement device. The player simulates an artillery shell trajectory on a CRT screen connected to an oscilloscope, with a set of knobs, the device uses purely analog electronics and does not use any digital computer or memory device or execute a program. It was patented by Thomas T. Goldsmith, Jr. and this, along with the lack of electronic logic circuits, keeps the device from being considered the first video game. Turing tested the code in a game in 1952 where he mimicked the operation of the code in a chess game against an opponent. The first publicly demonstrated electronic game was created in 1950, Bertie the Brain was an arcade game of tic-tac-toe, built by Josef Kates for the 1950 Canadian National Exhibition. To showcase his new miniature vacuum tube, the tube, he designed a specialized computer to use it. The game was a success at the exhibition, with attendees lining up to play it as Kates adjusted the difficulty up. After the exhibition, Bertie was dismantled, and largely forgotten as a novelty, Kates has said that he was working on so many projects at the same time that he had no energy to spare for preserving it, despite its significance. Using a panel of lights for its display, it was designed exclusively to play the game of Nim, Nimrod could play either the traditional or reverse form of the game

14.
Emulator
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In computing, an emulator is hardware or software that enables one computer system to behave like another computer system. An emulator typically enables the host system to run software or use peripheral devices designed for the guest system, emulation refers to the ability of a computer program in an electronic device to emulate another program or device. Many printers, for example, are designed to emulate Hewlett-Packard LaserJet printers because so much software is written for HP printers. If a non-HP printer emulates an HP printer, any software written for a real HP printer will also run in the non-HP printer emulation and produce equivalent printing. Since at least the 1990s until today, some video game enthusiasts use emulators to play 1980s arcade games using the original 1980s programming code, a hardware emulator is an emulator which takes the form of a hardware device. In a theoretical sense, the Church-Turing thesis implies that any operating environment can be emulated within any other environment. However, in practice, it can be difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. Emulation is a strategy in digital preservation to combat obsolescence, emulation addresses the original hardware and software environment of the digital object, and recreates it on a current machine. The emulator allows the user to have access to any kind of application or operating system on a current platform and he further states that this should not only apply to out of date systems, but also be upwardly mobile to future unknown systems. Potentially better graphics quality than original hardware, potentially additional features original hardware didnt have. Emulators maintain the look, feel, and behavior of the digital object. Despite the original cost of developing an emulator, it may prove to be the more cost efficient solution over time, many emulators have already been developed and released under GNU General Public License through the open source environment, allowing for wide scale collaboration. Emulators allow software exclusive to one system to be used on another, for example, a PlayStation 2 exclusive video game could be played on a PC using an emulator. This is especially useful when the system is difficult to obtain. Copyright laws are not yet in effect to address saving the documentation and these protections make it more difficult to design emulators, since they must be accurate enough to avoid triggering the protections, whose effects may not be obvious. Emulators require better hardware than the system has. Because of its use of digital formats, new media art relies heavily on emulation as a preservation strategy. The paradox is that the emulation and the emulator have to be made to work on future computers, emulation techniques are commonly used during the design and development of new systems

15.
Arcade game
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An arcade game or coin-op is a coin-operated entertainment machine typically installed in public businesses such as restaurants, bars and amusement arcades. Most arcade games are games, pinball machines, electro-mechanical games. While exact dates are debated, the age of arcade video games is usually defined as a period beginning sometime in the late 1970s. The old Midways of 1920s-era amusement parks provided the inspiration and atmosphere for later arcade games, in the 1930s the first coin-operated pinball machines emerged. These early amusement machines differed from their later electronic cousins in that they were made of wood and they lacked plungers or lit-up bonus surfaces on the playing field, and used mechanical instead of electronic scoring-readouts. By around 1977 most pinball machines in production switched to using solid-state electronics both for operation and for scoring, another Sega 1969 release, Missile, a shooter and vehicle-combat simulation, featured electronic sound and a moving film strip to represent the targets on a projection screen. In 1970 Midway released the game in North America as S. A. M. I, in the course of the 1970s, following the release of Pong in 1972, electronic video-games gradually replaced electro-mechanical arcade games. In 1972, Sega released a game called Killer Shark. In 1974, Nintendo released Wild Gunman, a shooter that used full-motion video-projection from 16 mm film to display live-action cowboy opponents on the screen. The 1978 video game Space Invaders, however, dealt a yet more powerful blow to the popularity of electro-mechanical games, in 1971 students at Stanford University set up the Galaxy Game, a coin-operated version of the Spacewar video game. This ranks as the earliest known instance of a video game. Later in the year, Nolan Bushnell created the first mass-manufactured game, Computer Space. In 1972, Atari was formed by Nolan Bushnell and Ted Dabney, Atari essentially created the coin-operated video game industry with the game Pong, the first successful electronic ping pong video game. Pong proved to be popular, but imitators helped keep Atari from dominating the fledgling coin-operated video game market, taitos Space Invaders, in 1978, proved to be the first blockbuster arcade video game. Its success marked the beginning of the age of arcade video games. Space Invaders, Galaxian, Pac-Man, Battlezone, Defender, by 1981, the arcade video game industry was worth $8 billion. By the late 1980s, the video game craze was beginning to fade due to advances in home video game console technology. By 1991, US arcade video game revenues had fallen to $2.1 billion, the pseudo-3D sprite/tile scaling was handled in a similar manner to textures in later texture-mapped polygonal 3D games of the 1990s

16.
Galaxy Game
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Galaxy Game is a space combat arcade game developed in 1971 as one of the last games created in the early history of video games. Galaxy Game is a version of the 1962 Spacewar. Potentially the first video game to spread to multiple computer installations and it features two spaceships, the needle and the wedge, engaged in a dogfight while maneuvering in the gravity well of a star. Both ships are controlled by human players and it charged players 10 cents per game or 25 cents for three, and drew crowds ten-deep. The pair built a prototype, replacing the first in the student union building in June 1972. It featured the capability to play multiple games simultaneously on four monitors and these consoles had a blue fiberglass casing, and the PDP-11 was housed inside one of the consoles. By the time of its installation, the pair had spent US$65,000 on the project, the second prototype remained in the student union building until 1979, when the display processor became faulty. It was restored and placed in the Stanford computer science department in 1997, then moved to the Computer History Museum in 2000, one of these games was Spacewar. Created in 1962 for the Digital Equipment Corporation PDP-1 minicomputer by Steve Russell, the two-player game has the players engage in a dogfight between two spaceships, set against the backdrop of a starfield, with a central star exerting gravitational force upon the ships. The original developers of Spacewar considered ways to monetize the game, fascinated by the computer and having taken several introductory computer classes, Pitts convinced the head of the project, Lester Earnest, to let him use the computer after hours. Soon, Pitts had ceased going to classes, instead spending his nights in the computer lab interacting with the graduate and postgraduate students, Pitts often played against Hugh Tuck, a student at California Polytechnic State University who was a friend from high school. During one Spacewar session that took place, depending on the source, such a device was still unfeasible due to the cost of computers, and the pair did not pursue the project. In 1971, however, Pitts, who by then had graduated and was working at Lockheed as a PDP-10 programmer, learned of the 1970 DEC PDP-11, the ships fire torpedoes, which are not affected by the gravitational pull of the star. The ships have a number of torpedoes and a limited supply of fuel. Torpedoes are fired one at a time, and there is a period between launches. The ships follow Newtonian physics, remaining in motion even when the player is not accelerating, each player controls one of the ships and must attempt to shoot down the other ship while avoiding a collision with the star. Flying near the star can provide a gravity assist to the player at the risk of misjudging the trajectory, if a ship moves past one edge of the screen, it reappears on the other side in a wraparound effect. Player controls include clockwise and counterclockwise rotation, forward thrust, firing torpedoes, the movement of the ships was controlled with a joystick, while the torpedoes, hyperspace, and game options are controlled via a panel of buttons

17.
Computer Space
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Computer Space is a space combat arcade game developed in 1971 as one of the last games created in the early history of video games. Created by Nolan Bushnell and Ted Dabney in partnership as Syzygy Engineering, Computer Space is a derivative of the 1962 computer game Spacewar. Possibly the first video game to spread to multiple computer installations and it features a rocket, controlled by the player, engaged in a missile battle with a pair of flying saucers set against a background starfield. The goal is to more hits than the enemy spaceships within a set time period. The game is enclosed in a fiberglass cabinet in one of four colors. The game was designed by Bushnell and Dabney during 1970–71 to be a version of Spacewar. After they built an early proof of concept and founded Syzygy Engineering, working in partnership with Nutting, the pair ran their first location test in August 1971, one month prior to the display of a similar prototype called Galaxy Game, also based on Spacewar. After encouraging initial results, though mixed responses from distributors, Nutting ordered a production run of 1,500 units with the anticipation of a hit game. The game spawned one clone game, Star Trek, and Nutting produced a version of Computer Space in 1973 without involvement from Syzygy before closing in 1976. Syzygy went on to be incorporated as Atari, with their arcade game the successful Pong. Although not as influential as Pong, Computer Spaces release marked the start of the commercial video game industry. One of these games was Spacewar, created in 1962 for the Digital Equipment Corporation PDP-1 minicomputer by Steve Russell and others in the programming community at the Massachusetts Institute of Technology. The two-player game has the players engage in a dogfight between two spaceships, set against the backdrop of a starfield, with a central star exerting gravitational force upon the ships. The original developers of Spacewar considered ways to monetize the game, the first commercial video game based on Spacewar would not be released until Computer Space in 1971. In Computer Space, the controls a rocket as it attempts to shoot a pair of flying saucers while avoiding enemy fire. The monochrome game has the three ships flying on a plane, set against the backdrop of a starfield. Missiles are fired one at a time, and there is a period between launches. The players rocket follows Newtonian physics, remaining in motion even when the player is not accelerating, the flying saucers stay in place or glide in a zig-zag pattern around the screen in tandem, with one staying a constant distance directly below the other

18.
Asteroids (video game)
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Asteroids is an arcade space shooter released in November 1979 by Atari, Inc. and designed by Lyle Rains, Ed Logg, and Dominic Walsh. The player controls a spaceship in a field which is periodically traversed by flying saucers. The object of the game is to shoot and destroy asteroids, the game becomes harder as the number of asteroids increases. Asteroids was one of the first major hits of the age of arcade games. The game sold over 70,000 arcade cabinets and proved popular with players and influential with developers. It has since been ported to multiple platforms, Asteroids was widely imitated and directly influenced Defender, Gravitar, and many other video games. Asteroids was conceived during a meeting between Logg and Rains and used hardware developed by Howard Delman previously used for Lunar Lander, based on an unfinished game titled Cosmos and inspired by Spacewar. Computer Space, and Space Invaders, Asteroids physics model, control scheme and gameplay theme were derived from earlier games and refined through trial. The game is rendered on a display in a two-dimensional view that wraps around in both screen axes. The objective of Asteroids is to destroy asteroids and saucers, the player controls a triangular ship that can rotate left and right, fire shots straight forward, and thrust forward. Once the ship begins moving in a direction, it continue in that direction for a time without player intervention unless the player applies thrust in a different direction. The ship eventually comes to a stop when not thrusting, the player can also send the ship into hyperspace, causing it to disappear and reappear in a random location on the screen, at the risk of self-destructing or appearing on top of an asteroid. Each level starts with a few large asteroids drifting in various directions on the screen, objects wrap around screen edges – for instance, an asteroid that drifts off the top edge of the screen reappears at the bottom and continues moving in the same direction. As the player shoots asteroids, they break into smaller asteroids that move faster and are difficult to hit. Smaller asteroids are also worth more points, two flying saucers appear periodically on the screen, the big saucer shoots randomly and poorly, while the small saucer fires frequently at the ship. After reaching a score of 40,000, only the small saucer appears, as the players score increases, the angle range of the shots from the small saucer diminishes until the saucer fires extremely accurately. Once the screen has been cleared of all asteroids and flying saucers, the game gets harder as the number of asteroids increases until after the score reaches a range between 40,000 and 60,000. The player starts with 3 lives after a coin is inserted, when the player loses all his lives, the game ends

19.
Library of Congress
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The Library of Congress is the research library that officially serves the United States Congress and is the de facto national library of the United States. It is the oldest federal cultural institution in the United States, the Library is housed in three buildings on Capitol Hill in Washington, D. C. it also maintains the Packard Campus in Culpeper, Virginia, which houses the National Audio-Visual Conservation Center. The Library of Congress claims to be the largest library in the world and its collections are universal, not limited by subject, format, or national boundary, and include research materials from all parts of the world and in more than 450 languages. Two-thirds of the books it acquires each year are in other than English. The Library of Congress moved to Washington in 1800, after sitting for years in the temporary national capitals of New York. John J. Beckley, who became the first Librarian of Congress, was two dollars per day and was required to also serve as the Clerk of the House of Representatives. The small Congressional Library was housed in the United States Capitol for most of the 19th century until the early 1890s, most of the original collection had been destroyed by the British in 1814, during the War of 1812. To restore its collection in 1815, the bought from former president Thomas Jefferson his entire personal collection of 6,487 books. After a period of growth, another fire struck the Library in its Capitol chambers in 1851, again destroying a large amount of the collection. The Library received the right of transference of all copyrighted works to have two copies deposited of books, maps, illustrations and diagrams printed in the United States. It also began to build its collections of British and other European works and it included several stories built underground of steel and cast iron stacks. Although the Library is open to the public, only high-ranking government officials may check out books, the Library promotes literacy and American literature through projects such as the American Folklife Center, American Memory, Center for the Book, and Poet Laureate. James Madison is credited with the idea for creating a congressional library, part of the legislation appropriated $5,000 for the purchase of such books as may be necessary for the use of Congress. And for fitting up an apartment for containing them. Books were ordered from London and the collection, consisting of 740 books and 3 maps, was housed in the new Capitol, as president, Thomas Jefferson played an important role in establishing the structure of the Library of Congress. The new law also extended to the president and vice president the ability to borrow books and these volumes had been left in the Senate wing of the Capitol. One of the only congressional volumes to have survived was a government account book of receipts and it was taken as a souvenir by a British Commander whose family later returned it to the United States government in 1940. Within a month, former president Jefferson offered to sell his library as a replacement

20.
TX-0
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The TX-0 was built in 1955 and went online in 1956 and was used continually through the 1960s at MIT. The transistorized TX-0 computer used 3600 transistors in its computers circuitry and had used the Philco high-frequency surface-barrier transistors in its design. In 1953, Philco had developed the worlds first high frequency surface-barrier transistor, the TX-0 and its direct descendant, the original PDP-1, were platforms for pioneering computer research and the development of what would later be called computer hacker culture. While the Whirlwind filled an entire floor of a building, TX-0 fit in a single reasonably sized room. The TX-0 was an 18-bit computer with a 16-bit address range, first two bits of machine word designate instruction and remaining 16 bits are used to specify memory location or operand for special operate instruction. First two bits could create four possible instructions, which included store, add, and conditional branch instructions as a basic set. The fourth instruction, operate, took additional operands and allowed access to a number of micro-orders which could be used separately or together to many other useful instructions. An add instruction took 10 microseconds, wesley A. Clark designed the logic and Ken Olsen oversaw the engineering development. With the successful completion of the TX-0, work turned immediately to the much larger, however this project soon ran into difficulties due to its complexity, and was redesigned into a smaller form that would eventually be delivered as the TX-2 in 1958. Since core memory was expensive at the time, several parts of the TX-0 memory were cannibalized for the TX-2 project. Delivered from Lincoln Laboratory with only 4K of core, the no longer needed 16 bits to represent a storage address. After about a year and a half, the number of bits was doubled to four, allowing a total of 16 instructions. This dramatically improved programmability of the machine, but still left room for a memory expansion to 8K. Meanwhile the TX-2 project was running into difficulties of its own, a year later, DEC donated the engineering prototype PDP-1 machine to MIT. It was installed in the next to TX-0, and the two machines would run side-by-side for almost a decade. Significant pieces of the TX-0 are currently on display in the Library at Lincoln Laboratory, the library is only accessible to Lincoln Lab employees. In 1983, the TX-0 was still running and is running a maze application in the first episode of Computer Chronicles. Dennis, Charles Babbage Institute, University of Minnesota, the TX-0, Its Past and Present TX-0 documentation TX-0 programs Steven Levy, Hackers, Heroes of the Computer Revolution Welcome

21.
Light pen
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A light pen is a computer input device in the form of a light-sensitive wand used in conjunction with a computers CRT display. It allows the user to point to displayed objects or draw on the screen in a way to a touchscreen. A light pen can work with any CRT-based display and other display technologies, a light pen detects a change of brightness of nearby screen pixels when scanned by cathode ray tube electron beam and communicates the timing of this event to the computer. The first light pen was created around 1955 as part of the Whirlwind project at MIT, during the 1960s light pens were common on graphics terminals such as the IBM2250, and were also available for the IBM3270 text-only terminal. Light pen usage was expanded in the early 1980s to personal computers such as the Fairlight CMI, and the BBC Micro

22.
Tic-tac-toe
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Tic-tac-toe is a paper-and-pencil game for two players, X and O, who take turns marking the spaces in a 3×3 grid. The player who succeeds in placing three of their marks in a horizontal, vertical, or diagonal row wins the game, the following example game is won by the first player, X, Players soon discover that best play from both parties leads to a draw. Hence, tic-tac-toe is most often played by young children. The game can be generalized to an m, n, k-game in which two players alternate placing stones of their own color on an m×n board, with the goal of getting k of their own color in a row. Hararys generalized tic-tac-toe is an even broader generalization of tic tac toe and it can also be generalized as a nd game. Tic-tac-toe is the game where n equals 3 and d equals 2, according to Claudia Zaslavskys book Tic Tac Toe, And Other Three-In-A Row Games from Ancient Egypt to the Modern Computer, tic-tac-toe could be traced back to ancient Egypt. Another closely related ancient game is Three Mens Morris which is played on a simple grid. An early variation of tic-tac-toe was played in the Roman Empire and it was called Terni Lapilli and instead of having any number of pieces, each player only had three, thus they had to move them around to empty spaces to keep playing. The games grid markings have been found chalked all over Rome, the different names of the game are more recent. The first print reference to noughts and crosses, the British name, in his novel Can You Forgive Her,1864, Anthony Trollope refers to a clerk playing tit-tat-toe. Tic-tac-toe may also derive from tick-tack, the name of an old version of backgammon first described in 1558, the U. S. renaming of Noughts and crosses as tic-tac-toe occurred in the 20th century. In 1952, OXO, developed by British computer scientist Alexander S. Douglas for the EDSAC computer at the University of Cambridge, the computer player could play perfect games of tic-tac-toe against a human opponent. In 1975, tic-tac-toe was also used by MIT students to demonstrate the power of Tinkertoy elements. The Tinkertoy computer, made out of only Tinkertoys, is able to play tic-tac-toe perfectly and it is currently on display at the Museum of Science, Boston. A position is merely a state of the board, while a game usually refers to the way a position is obtained. Naive counting leads to 19,683 possible board layouts, and 362,880 possible games, however, two matters much reduce these numbers, The game ends when three-in-a-row is obtained. If X starts, the number of Xs is always equal to or exactly 1 more than the number of Os. The complete analysis is complicated by the definitions used when setting the conditions

23.
Minicomputer
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A minicomputer, or colloquially mini, is a class of smaller computers that developed in the mid-1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors. The class formed a group with its own software architectures. Minis were designed for control, instrumentation, human interaction, and communication switching as distinct from calculation, many were sold indirectly to Original Equipment Manufacturers for final end use application. During the two decade lifetime of the class, almost 100 companies formed and only a half dozen remained. They usually took up one or a few 19-inch rack cabinets, the definition of minicomputer is vague with the consequence that there are a number of candidates for the first minicomputer. An early and highly successful minicomputer was Digital Equipment Corporations 12-bit PDP-8, later versions of the PDP-8 took advantage of small-scale integrated circuits. The important precursors of the PDP-8 include the PDP-5, LINC, the TX-0, the TX-2, DEC gave rise to a number of minicomputer companies along Massachusetts Route 128, including Data General, Wang Laboratories, Apollo Computer, and Prime Computer. Minicomputers were also known as midrange computers and they grew to have relatively high processing power and capacity. They were used in manufacturing process control, telephone switching and to control laboratory equipment, in the 1970s, they were the hardware that was used to launch the computer-aided design industry and other similar industries where a smaller dedicated system was needed. The 7400 series of TTL integrated circuits started appearing in minicomputers in the late 1960s, the 74181 arithmetic logic unit was commonly used in the CPU data paths. Each 74181 had a bus width of four bits, hence the popularity of bit-slice architecture, some scientific computers, such as the Nicolet 1080, would use the 7400 series in groups of five ICs for their uncommon twenty bits architecture. Starting in the 1980s, many minicomputers used VLSI circuits, the result was that minicomputers and computer terminals were replaced by networked workstations, file servers and PCs in some installations, beginning in the latter half of the 1980s. Also, the Microsoft Windows series of operating systems, beginning with Windows NT, now included server versions that supported preemptive multitasking, Digital Equipment Corporation was once the leading minicomputer manufacturer, at one time the second-largest computer company after IBM. DEC was sold to Compaq in 1998, while Data General was acquired by EMC Corporation, today only a few proprietary minicomputer architectures survive. The IBM System/38 operating system, which introduced many advanced concepts, realising the importance of the myriad lines of legacy code written, AS stands for Application System. Great efforts were made by IBM to enable programs written for the System/34. The AS/400 was replaced by the iSeries, which was replaced by the System i. In 2008, the System i was replaced by the IBM Power Systems, by contrast, competing proprietary computing architectures from the early 1980s, such as DECs VAX, Wang VS and Hewlett Packards HP3000 have long been discontinued without a compatible upgrade path

24.
Kludge
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A kludge is a workaround or quick-and-dirty solution that is clumsy, inelegant, inefficient, difficult to extend and hard to maintain. This term is used in fields such as computer science, aerospace engineering, Internet slang, evolutionary neuroscience. The word has alternate spellings, pronunciations and several proposed etymologies, although OED accepts Granholms definition and credits him with the invention, examples of its use before the 1960s exist. A source of confusion has been Granholms jocular citation of the wholly fictitious lexicographer, Phineas Burling, of the firm Fink. A phone call to Phineas Burling can be revealing, Phineas Burling is the Chief calligrapher with the Fink and Wiggles Publishing Company, Inc. Fink and Wiggles are, of course, the well known publishers of the NEW MULTILINGUAL DICTIONARY. According to Burling, the word kludge first appeared in the English language in the early fifteen-hundreds and it was imported into the geographic region of the lowlands between Kings Lynn and the Isle of Ely by Dutch settlers arriving there to reclaim tidelands of the Wash as rutabaga fields. The word kludge is, according to Burling, derived from the root as the German klug. In the typical machinations of language in evolutionary growth, the word Kludge eventually came to not so smart or pretty ridiculous. Today the leading definition given by the NEW MULTILINGUAL is, An ill-assorted collection of poorly-matching parts and it is in this latter sense that Kludge is used by computer hardware men. Today kludge forms one of the most beloved words in design terminology, the building of a Kludge, however, is not work for amateurs. There is a certain, indefinable, masochistic finesse that must go into true Kludge building, the professional can spot it instantly. The amateur may readily presume that thats the way computers are and this may explain the idea of clever but clumsy and temporary, as well as the pronunciation variation from German. It may instead derive from the mispronunciation of European surname Kluge and this OED2 entry also includes the verb kludge to improvise with a kludge or kludges and kludgemanship skill in designing or applying kludges. The Jargon File, which is a glossary of computer programmer slang maintained by Eric S. Raymond, differentiates kludge from kluge and these two words have been confused in American usage since the early 1960s, and widely confounded in Great Britain since the end of World War II. To use a kludge to get around a problem, ive kludged around it for now, but Ill fix it up properly later. A Rube Goldberg device, whether in hardware or software, a clever programming trick intended to solve a particular nasty case in an expedient, if not clear, manner. Often involves ad-hockery and verges on being a crock, something that works for the wrong reason. To insert a kluge into a program, ive kluged this routine to get around that weird bug, but theres probably a better way

25.
Harvard University
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Although never formally affiliated with any denomination, the early College primarily trained Congregationalist and Unitarian clergy. Its curriculum and student body were gradually secularized during the 18th century, james Bryant Conant led the university through the Great Depression and World War II and began to reform the curriculum and liberalize admissions after the war. The undergraduate college became coeducational after its 1977 merger with Radcliffe College, Harvards $34.5 billion financial endowment is the largest of any academic institution. Harvard is a large, highly residential research university, the nominal cost of attendance is high, but the Universitys large endowment allows it to offer generous financial aid packages. Harvards alumni include eight U. S. presidents, several heads of state,62 living billionaires,359 Rhodes Scholars. To date, some 130 Nobel laureates,18 Fields Medalists, Harvard was formed in 1636 by vote of the Great and General Court of the Massachusetts Bay Colony. In 1638, it obtained British North Americas first known printing press, in 1639 it was named Harvard College after deceased clergyman John Harvard an alumnus of the University of Cambridge who had left the school £779 and his scholars library of some 400 volumes. The charter creating the Harvard Corporation was granted in 1650 and it offered a classic curriculum on the English university model‍—‌many leaders in the colony had attended the University of Cambridge‍—‌but conformed to the tenets of Puritanism. It was never affiliated with any denomination, but many of its earliest graduates went on to become clergymen in Congregational. The leading Boston divine Increase Mather served as president from 1685 to 1701, in 1708, John Leverett became the first president who was not also a clergyman, which marked a turning of the college toward intellectual independence from Puritanism. When the Hollis Professor of Divinity David Tappan died in 1803 and the president of Harvard Joseph Willard died a year later, in 1804, in 1846, the natural history lectures of Louis Agassiz were acclaimed both in New York and on the campus at Harvard College. Agassizs approach was distinctly idealist and posited Americans participation in the Divine Nature, agassizs perspective on science combined observation with intuition and the assumption that a person can grasp the divine plan in all phenomena. When it came to explaining life-forms, Agassiz resorted to matters of shape based on an archetype for his evidence. Charles W. Eliot, president 1869–1909, eliminated the position of Christianity from the curriculum while opening it to student self-direction. While Eliot was the most crucial figure in the secularization of American higher education, he was motivated not by a desire to secularize education, during the 20th century, Harvards international reputation grew as a burgeoning endowment and prominent professors expanded the universitys scope. Rapid enrollment growth continued as new schools were begun and the undergraduate College expanded. Radcliffe College, established in 1879 as sister school of Harvard College, Harvard became a founding member of the Association of American Universities in 1900. In the early 20th century, the student body was predominately old-stock, high-status Protestants, especially Episcopalians, Congregationalists, by the 1970s it was much more diversified

26.
Cambridge, Massachusetts
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Cambridge is a city in Middlesex County, Massachusetts, and is a part of the Boston metropolitan area. According to the 2010 Census, the population was 105,162. As of July 2014, it was the fifth most populous city in the state, behind Boston, Worcester, Springfield, Cambridge was one of the two seats of Middlesex County prior to the abolition of county government in 1997, Lowell was the other. The site for what would become Cambridge was chosen in December 1630, because it was located safely upriver from Boston Harbor, Thomas Dudley, his daughter Anne Bradstreet, and her husband Simon, were among the first settlers of the town. The first houses were built in the spring of 1631, the settlement was initially referred to as the newe towne. Official Massachusetts records show the name capitalized as Newe Towne by 1632, the original village site is in the heart of todays Harvard Square. In the late 19th century, various schemes for annexing Cambridge itself to the city of Boston were pursued and rejected, in 1636, the Newe College was founded by the colony to train ministers. Newe Towne was chosen for the site of the college by the Great and General Court primarily—according to Cotton Mather—to be near the popular, in May 1638 the name of the settlement was changed to Cambridge in honor of the university in Cambridge, England. Hooker and Shepard, Newtownes ministers, and the colleges first president, major benefactor, in 1629, Winthrop had led the signing of the founding document of the city of Boston, which was known as the Cambridge Agreement, after the university. It was Governor Thomas Dudley who, in 1650, signed the charter creating the corporation which still governs Harvard College, Cambridge grew slowly as an agricultural village eight miles by road from Boston, the capital of the colony. By the American Revolution, most residents lived near the Common and Harvard College, with farms and estates comprising most of the town. Coming up from Virginia, George Washington took command of the volunteer American soldiers camped on Cambridge Common on July 3,1775, most of the Tory estates were confiscated after the Revolution. On January 24,1776, Henry Knox arrived with artillery captured from Fort Ticonderoga, a second bridge, the Canal Bridge, opened in 1809 alongside the new Middlesex Canal. The new bridges and roads made what were formerly estates and marshland into prime industrial and residential districts, in the mid-19th century, Cambridge was the center of a literary revolution when it gave the country a new identity through poetry and literature. Cambridge was home to some of the famous Fireside Poets—so called because their poems would often be read aloud by families in front of their evening fires, the Fireside Poets—Henry Wadsworth Longfellow, James Russell Lowell, and Oliver Wendell Holmes—were highly popular and influential in their day. Cambridge was incorporated as a city in 1846, the citys commercial center began to shift from Harvard Square to Central Square, which became the downtown of the city around this time. The coming of the railroad to North Cambridge and Northwest Cambridge then led to three changes in the city, the development of massive brickyards and brickworks between Massachusetts Ave. For many decades, the citys largest employer was the New England Glass Company, by the middle of the 19th century it was the largest and most modern glassworks in the world

27.
Rolling Stone
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Rolling Stone is an American biweekly magazine that focuses on popular culture. It was founded in San Francisco in 1967 by Jann Wenner, who is still the publisher. It was first known for its coverage and for political reporting by Hunter S. Thompson. In the 1990s, the magazine shifted focus to a readership interested in youth-oriented television shows, film actors. In recent years, it has resumed its traditional mix of content, Rolling Stone magazine was founded in San Francisco in 1967 by Jann Wenner and Ralph Gleason. To get it off the ground, Wenner borrowed $7,500 from his own family and from the parents of his soon-to-be wife, Jane Schindelheim. The first issue carried a date of November 9,1967. Some authors have attributed the name solely to Dylans hit single, At Gleasons suggestion, Rolling Stone initially identified with and reported the hippie counterculture of the era. In the very first edition, Wenner wrote that Rolling Stone is not just about the music, in the 1970s, Rolling Stone began to make a mark with its political coverage, with the likes of gonzo journalist Hunter S. Thompson writing for the magazines political section. Thompson first published his most famous work Fear and Loathing in Las Vegas within the pages of Rolling Stone, where he remained a contributing editor until his death in 2005. In the 1970s, the magazine also helped launch the careers of prominent authors, including Cameron Crowe, Lester Bangs, Joe Klein, Joe Eszterhas, Patti Smith. It was at point that the magazine ran some of its most famous stories. One interviewer, speaking for a number of his peers, said that he bought his first copy of the magazine upon initial arrival on his college campus. In 1977, the magazine moved its headquarters from San Francisco to New York City, editor Jann Wenner said San Francisco had become a cultural backwater. During the 1980s, the magazine began to shift towards being an entertainment magazine. Music was still a dominant topic, but there was increasing coverage of celebrities in television, films, the magazine also initiated its annual Hot Issue during this time. Rolling Stone was initially known for its coverage and for Thompsons political reporting. In the 1990s, the changed its format to appeal to a younger readership interested in youth-oriented television shows, film actors

28.
Marvin Minsky
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Marvin Lee Minsky was born in New York City, to an eye surgeon father, Henry, and to a mother, Fannie, who was an activist of Zionist affairs. He attended the Ethical Culture Fieldston School and the Bronx High School of Science and he later attended Phillips Academy in Andover, Massachusetts. He then served in the US Navy from 1944 to 1945 and he received a B. A. in mathematics from Harvard University and a Ph. D. in mathematics from Princeton University. He was on the MIT faculty from 1958 to his death, in 1959 he and John McCarthy initiated what is known now as the MIT Computer Science and Artificial Intelligence Laboratory. He was the Toshiba Professor of Media Arts and Sciences, and professor of electrical engineering, Minskys inventions include the first head-mounted graphical display and the confocal microscope. He developed, with Seymour Papert, the first Logo turtle, Minsky also built, in 1951, the first randomly wired neural network learning machine, SNARC. Minsky wrote the book Perceptrons, which became the work in the analysis of artificial neural networks. He also founded several other famous AI models and his book A framework for representing knowledge created a new paradigm in programming. While his Perceptrons is now more a historical than practical book, Minsky has also written on the possibility that extraterrestrial life may think like humans, permitting communication. Clarkes derivative novel of the name, Probably no one would ever know this. In the 1980s, Minsky and Good had shown how neural networks could be generated automatically—self replicated—in accordance with any arbitrary learning program, Artificial brains could be grown by a process strikingly analogous to the development of a human brain. In any given case, the details would never be known. In the early 1970s, at the MIT Artificial Intelligence Lab, Minsky, the theory attempts to explain how what we call intelligence could be a product of the interaction of non-intelligent parts. Minsky says that the biggest source of ideas about the theory came from his work in trying to create a machine that uses an arm, a video camera. In 1986, Minsky published The Society of Mind, a book on the theory which. Recent drafts of the book are available from his webpage. In 1952, Minsky married pediatrician Dr. Gloria Rudisch, together they had three children, Minsky was a talented improvisational pianist who published musings on the relations between music and psychology. Minsky was an atheist and a signatory to the Scientists Open Letter on Cryonics and he was a critic of the Loebner Prize for conversational robots

29.
Kaleidoscope
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The reflectors are usually enclosed in a tube, often containing on one end a cell with loose, colored pieces of glass or other transparent materials to be reflected into the viewed pattern. Rotation of the cell causes motion of the materials, resulting in an ever changing viewed pattern, a kaleidoscope operates on the principle of multiple reflection, where two or more reflectors are placed at an angle to one another. When the eye is placed at one end of the reflectors, for irregular objects situated at any position the angle should be an even aliquot part of 360°. The reflected object should be in contact with the ends of the reflectors, the eye should be as near as possible to the angular point of the ends of the reflector opposite the reflected object. An object-box on the ends of the reflectors can hold selected objects to be viewed in the reflected pattern, colorful transparent shapes to create beautiful patterns. Objects smaller than the aperture create an appearance of the pattern. Larger opaque objects and darker colors dont transmit much light and are usually avoided, if objects, fragments and/or liquids are loosely placed inside the cell and tumble when the cell is rotated, motion and change of colors and shapes can be introduced into the viewed pattern. Multiple reflection by two or more reflecting surfaces has been known since antiquity and was described by as such by Giambattista della Porta in his Magia Naturalis. Mr. Bradleys New Improvements in Planting and Gardening described a similar construction to be placed on geometrical drawings to show an image with multiplied reflection, however, an optimal configuration that produces the full effects of the kaleidoscope have not been recorded before 1815. He forgot about it, but noticed a more impressive version of the effect during experiments in February 1815. This triggered more experiments to find the conditions for the most beautiful, a version followed in which some of the objects and pieces of glass could move when the tube was rotated. The last step, regarded as most important by Brewster, was to place the reflecting panes in a tube with a concave lens to distinctly introduce surrounding objects into the reflected pattern. Brewster thought his instrument to be of value in all the ornamental arts as a device that creates an infinity of patterns. Artists could accurately delineate the produced figures of the kaleidoscope by means of the solar micoscope, Brewster believed it would at the same time become a popular instrument for the purposes of rational amusement. He decided to apply for a patent, british patent no.4136 for a new Optical Instrument called The Kaleidoscope for exhibiting and creating beautiful Forms and Patterns of great use in all the ornamental Arts was granted in July 1817. Unfortunately the manufacturer originally engaged to produce the product had one of the patent instruments to some of the London opticians to see if he could get orders from them. Soon the instrument was copied and marketed before the manufacturer had prepared any number of kaleidoscopes for sale, an estimated two hundred thousand kaleidoscopes sold in London and Paris in just three months. Brewster figured at most a thousand of these were authorized copies that were constructed correctly and it was thought that the patent was reduced in a Court of Law since its principles were supposedly already known

30.
Spacecraft
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A spacecraft is a vehicle, or machine designed to fly in outer space. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, space colonization, planetary exploration, on a sub-orbital spaceflight, a spacecraft enters space and then returns to the surface, without having gone into an orbit. For orbital spaceflights, spacecraft enter closed orbits around the Earth or around other celestial bodies, robotic spacecraft used to support scientific research are space probes. Robotic spacecraft that remain in orbit around a body are artificial satellites. Only a handful of interstellar probes, such as Pioneer 10 and 11, Voyager 1 and 2, orbital spacecraft may be recoverable or not. By method of reentry to Earth they may be divided in non-winged space capsules, Sputnik 1 was the first artificial satellite. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957, the launch ushered in new political, military, technological, and scientific developments, while the Sputnik launch was a single event, it marked the start of the Space Age. Apart from its value as a technological first, Sputnik 1 also helped to identify the upper atmospheric layers density and it also provided data on radio-signal distribution in the ionosphere. Pressurized nitrogen in the satellites false body provided the first opportunity for meteoroid detection, Sputnik 1 was launched during the International Geophysical Year from Site No. 1/5, at the 5th Tyuratam range, in Kazakh SSR. The satellite travelled at 29,000 kilometers per hour, taking 96.2 minutes to complete an orbit and this altitude is called the Kármán line. In particular, in the 1940s there were several test launches of the V-2 rocket, as of 2016, only three nations have flown manned spacecraft, USSR/Russia, USA, and China. The first manned spacecraft was Vostok 1, which carried Soviet cosmonaut Yuri Gagarin into space in 1961, there were five other manned missions which used a Vostok spacecraft. The second manned spacecraft was named Freedom 7, and it performed a sub-orbital spaceflight in 1961 carrying American astronaut Alan Shepard to an altitude of just over 187 kilometers, there were five other manned missions using Mercury spacecraft. Other Soviet manned spacecraft include the Voskhod, Soyuz, flown unmanned as Zond/L1, L3, TKS, China developed, but did not fly Shuguang, and is currently using Shenzhou. Except for the shuttle, all of the recoverable manned orbital spacecraft were space capsules. Manned space capsules The International Space Station, manned since November 2000, is a joint venture between Russia, the United States, Canada and several other countries, some reusable vehicles have been designed only for manned spaceflight, and these are often called spaceplanes. The first example of such was the North American X-15 spaceplane, the first reusable spacecraft, the X-15, was air-launched on a suborbital trajectory on July 19,1963. The first partially reusable spacecraft, a winged non-capsule, the Space Shuttle, was launched by the USA on the 20th anniversary of Yuri Gagarins flight

31.
Front panel
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A front panel was used on early electronic computers to display and allow the alteration of the state of the machines internal registers and memory. The front panel usually consisted of arrays of indicator lamps, toggle switches, in early machines, CRTs might also be present. Prior to the development of CRT system consoles, many such as the IBM1620 had console typewriters. Usually the contents of one or more registers would be represented by a row of lights. The switches allowed direct entry of data and address values into registers or memory, on some machines, certain lights and switches were reserved for use under program control. These were often referred to as sense lights and sense switches, for example, the original Fortran compiler for the IBM704 contained specific statements for testing and manipulation of the 704s sense lights and switches. These switches were used by the program to control optional behavior, for example information might be printed only if a particular sense switch was set. Operating systems made for computers with blinkenlights, for example, RSTS/E and RSX-11, system programmers often became very familiar with these light patterns and could tell from them how busy the system was and, sometimes, exactly what it was doing at the moment. The Master Control Program for the Burroughs Corporation B6700 mainframe would display a large block-letter B when the system was idle, switches and lights required little additional logic circuitry and usually no software support, important when logic hardware components were costly and software often limited. The 6600 had support from ten supporting peripheral processors whose duties included reading the keyboard, an operator would use the front panel to bootstrap the computer, to debug running programs, and to find hardware faults. Typically, the operator would have a written procedure containing a series of bootstrap instructions that would be hand-entered using the toggle switches. First, the operator would set the switch and enter the address in binary using the switches. For easier entry and readout, on some computers binary digits were grouped into threes on the front panel, decimal computers like the IBM1620 used binary-coded decimal for memory addresses. Next the operator would set the switch, and then enter the value intended for that address. After entering several of these instructions, the operator would set the starting address of the bootstrap program. The bootstrap program usually read a somewhat longer program from punched paper-tape, punched cards, some machines accelerated the bootstrap process by allowing the operator to set the switches to contain one or two machine language instructions and then directly executing those instructions. Other machines allowed I/O devices to be commanded from the front panel. Some machines also contained various bootstrap programs in ROM and all that was required to boot the system was to start it executing at the address of the correct ROM program

32.
Cathode ray tube
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The cathode ray tube is a vacuum tube that contains one or more electron guns and a phosphorescent screen, and is used to display images. It modulates, accelerates, and deflects electron beam onto the screen to create the images, the images may represent electrical waveforms, pictures, radar targets, or others. CRTs have also used as memory devices, in which case the visible light emitted from the fluorescent material is not intended to have significant meaning to a visual observer. In television sets and computer monitors, the front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. An image is produced by controlling the intensity of each of the three beams, one for each additive primary color with a video signal as a reference. A CRT is constructed from an envelope which is large, deep, fairly heavy. The interior of a CRT is evacuated to approximately 0.01 Pa to 133 nPa. evacuation being necessary to facilitate the flight of electrons from the gun to the tubes face. That it is evacuated makes handling an intact CRT potentially dangerous due to the risk of breaking the tube and causing a violent implosion that can hurl shards of glass at great velocity. As a matter of safety, the face is made of thick lead glass so as to be highly shatter-resistant and to block most X-ray emissions. Flat panel displays can also be made in large sizes, whereas 38 to 40 was about the largest size of a CRT television, flat panels are available in 60. Cathode rays were discovered by Johann Hittorf in 1869 in primitive Crookes tubes and he observed that some unknown rays were emitted from the cathode which could cast shadows on the glowing wall of the tube, indicating the rays were traveling in straight lines. In 1890, Arthur Schuster demonstrated cathode rays could be deflected by electric fields, the earliest version of the CRT was known as the Braun tube, invented by the German physicist Ferdinand Braun in 1897. It was a diode, a modification of the Crookes tube with a phosphor-coated screen. In 1907, Russian scientist Boris Rosing used a CRT in the end of an experimental video signal to form a picture. He managed to display simple geometric shapes onto the screen, which marked the first time that CRT technology was used for what is now known as television. The first cathode ray tube to use a hot cathode was developed by John B. Johnson and Harry Weiner Weinhart of Western Electric and it was named by inventor Vladimir K. Zworykin in 1929. RCA was granted a trademark for the term in 1932, it released the term to the public domain in 1950. The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934, in oscilloscope CRTs, electrostatic deflection is used, rather than the magnetic deflection commonly used with television and other large CRTs

33.
Vint Cerf
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Vinton Gray Cerf ForMemRS, is an American Internet pioneer, who is recognized as one of the fathers of the Internet, sharing this title with TCP/IP co-inventor Bob Kahn. In the early days, Cerf was a manager for the United States Defense Advanced Research Projects Agency funding various groups to develop TCP/IP technology, Cerf was instrumental in the funding and formation of ICANN from the start. He waited in the wings for a year before he stepped forward to join the ICANN Board and he was elected as the president of the Association for Computing Machinery in May 2012, and in August 2013 he joined the Council on CyberSecuritys Board of Advisors. Cerf is active in organizations that are working to help the Internet deliver humanitarian value in our world today. He is supportive of innovative projects that are experimenting with new approaches to problems, including the digital divide, the gender gap. Cerf is also known for his style, typically appearing in a three-piece suit—a rarity in an industry known for its casual dress norms. Cerf was born in New Haven, Connecticut, the son of Muriel, a housewife, and Vinton Thruston Cerf, Cerf went to Van Nuys High School in California along with Jon Postel and Steve Crocker, he wrote the formers obituary. Both were also instrumental in the creation of the Internet, whilst in high school, Cerf worked at Rocketdyne on the Apollo program, including helping to write statistical analysis software for the non-destructive tests of the F-1 engines. Cerfs first job after obtaining his B. S. degree in mathematics from Stanford University was at IBM and he left IBM to attend graduate school at UCLA where he earned his M. S. degree in 1970 and his PhD degree in 1972. While at UCLA, he also met Bob Kahn, who was working on the ARPANet hardware architecture, Cerf then moved to DARPA in 1976, where he stayed until 1982. As vice president of MCI Digital Information Services from 1982 to 1986, Cerf led the engineering of MCI Mail, the first commercial email service to be connected to the Internet. In 1986, he joined Bob Kahn at the Corporation for National Research Initiatives as its president, working with Kahn on Digital Libraries, Knowledge Robots. It was during time, in 1992, that he and Kahn, among others, founded the Internet Society to provide leadership in education, policy. Cerf served as the first president of ISOC, Cerf rejoined MCI during 1994 and served as Senior Vice President of Technology Strategy. In this role, he helped to guide corporate strategy development from a technical perspective, during 1997, Cerf joined the Board of Trustees of Gallaudet University, a university for the education of the deaf and hard-of-hearing. Cerf himself is hard of hearing and he has also served on the universitys Board of Associates. Cerf, as leader of MCIs internet business, was criticized due to MCIs role in providing the IP addresses used by Send-Safe. com, MCI refused to terminate the spamware vendor. At the time, Spamhaus also listed MCI as the ISP with the most Spamhaus Block List listings, Cerf has worked for Google as a Vice President and Chief Internet Evangelist since October 2005

34.
Computer History Museum
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The Computer History Museum is a museum established in 1996 in Mountain View, California, US. The Museum is dedicated to preserving and presenting the stories and artifacts of the information age, the museums origins date to 1968 when Gordon Bell began a quest for a historical collection and, at that same time, others were looking to preserve the Whirlwind computer. The resulting Museum Project had its first exhibit in 1975, located in a coat closet in a DEC lobby. In 1978, the museum, now The Digital Computer Museum, moved to a larger DEC lobby in Marlborough, maurice Wilkes presented the first lecture at TDCM in 1979 – the presentation of such lectures has continued to the present time. TDCM incorporated as The Computer Museum in 1982, in 1984, TCM moved to Boston, locating on Museum Wharf. In 1996/1997, The TCM History Center in Silicon Valley was established, a site at Moffett Field was provided by NASA, in 1999, TCMHC incorporated and TCM ceased operation, shipping its remaining artifacts to TCMHC in 2000. The name TCM had been retained by the Boston Museum of Science so, in 2000, in 2003, CHM opened its new building, at 1401 N. Shoreline Blvd in Mountain View, California, to the public. The facility was heavily renovated and underwent a two-year $19 million makeover before reopening on January 2011. The Computer History Museum claims to house the largest and most significant collection of computing artifacts in the world, the collection comprises nearly 90,000 objects, photographs and films, as well as 4,000 feet of cataloged documentation and several hundred gigabytes of software. The CHM oral history program conducts video interviews around the history of computing and networking, the museums 25, 000-square-foot exhibit Revolution, The First 2000 Years of Computing, opened to the public on January 13,2011. It covers the history of computing in 20 galleries, from the abacus to the Internet, the entire exhibition is also available online. The museum features a Liquid Galaxy in the “Going Places, A History of Silicon Valley” exhibit, the exhibit features 20 preselected locations that visitors can fly to on the Liquid Galaxy. An operating Difference Engine designed by Charles Babbage in the 1840s and it had been on loan since 2008 from its owner, Nathan Myhrvold, a former Microsoft executive. Former media executive John Hollar was appointed CEO of The Computer History Museum in July 2008, in 2012 the APL programming language followed. In February 2013 Adobe Systems, Inc. donated the Photoshop 1.0.1 source code to the collection, on October 21,2014, Xerox Altos source code and other resources followed. The CHM Fellows are exceptional men and women whose ideas have changed the world, the first fellow was Rear Admiral Grace Hopper in 1987. The fellows program has grown to 70 members as of 2015, vintage Computer Festival held annually at The Computer History Museum Computer museums History of computing History of computer science Bell, Gordon. Out of a Closet, The Early Years of the Computer * Museum, official website Computer History Museums channel on YouTube The Computer Museum Archive

35.
ICANN
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ICANN performs the actual technical maintenance work of the central Internet address pools and DNS root zone registries pursuant to the Internet Assigned Numbers Authority function contract. The numbering facilities ICANN manages include the Internet Protocol address spaces for IPv4 and IPv6, ICANN also maintains registries of Internet Protocol identifiers. ICANN was created on September 18,1998, and incorporated on September 30,1998 and it is headquartered in the Playa Vista neighborhood of Los Angeles. In 1997 Postel testified before Congress that this had come about as a task to this research work. The Information Sciences Institute was funded by the U. S. Department of Defense, as was SRI Internationals Network Information Center, which also performed some assigned name functions. As the Internet grew and expanded globally, the U. S. Department of Commerce initiated a process to establish a new organization to perform the IANA functions. The proposed rule making, or Green Paper, was published in the Federal Register on February 20,1998, NTIA received more than 650 comments as of March 23,1998, when the comment period closed. ICANN was formed in response to this policy, ICANN managed the Internet Assigned Numbers Authority under contract to the United States Department of Commerce and pursuant to an agreement with the IETF. ICANN was incorporated in California on September 30,1998, with entrepreneur and it is a nonprofit public benefit corporation organized under the California Nonprofit Public Benefit Corporation Law for charitable and public purposes. ICANN was established in California due to the presence of Jon Postel, ICANN formerly operated from the same Marina del Rey building where Postel formerly worked, which is home to an office of the Information Sciences Institute at the University of Southern California. However, ICANNs headquarters is now located in the nearby Playa Vista neighborhood of Los Angeles and they were also required to be financially independent from ICANN. On July 26,2006, the United States government renewed the contract with ICANN for performance of the IANA function for a one to five years. The context of ICANNs relationship with the U. S. government was clarified on September 29,2006 when ICANN signed a new Memorandum of Understanding with the United States Department of Commerce and this document gave the DOC oversight over some of the ICANN operations. During July 2008, the DOC reiterated a statement that it has no plans to transition management of the authoritative root zone file to ICANN. The letter also stresses the separate roles of the IANA and VeriSign, on September 30,2009, ICANN signed an agreement with the DOC that confirmed ICANNs commitment to a multistakeholder governance model, but did not remove it from DOC oversight and control. On March 10,2016, ICANN and the DOC signed a historic, culminating agreement to finally remove ICANN and IANA from the control, on October 1,2016, ICANN was freed from U. S. government oversight. During September and October 2003, ICANN played a role in the conflict over VeriSigns wild card DNS service Site Finder. After an open letter from ICANN issuing an ultimatum to VeriSign, later endorsed by the Internet Architecture Board, after this action, VeriSign filed a lawsuit against ICANN on February 27,2004, claiming that ICANN had exceeded its authority

36.
Lensman series
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The Lensman series is a serial science fiction space opera by American author Edward Elmer Doc Smith. It was a runner-up for the 1966 Hugo award for Best All-Time Series, the series was published in magazines, before being collected and reworked into the better-known series of books. The complete series in sequence with original publication dates is as follows. In 1948, at the suggestion of Lloyd Arthur Eshbach, Smith rewrote his 1934 story Triplanetary to fit in with the Lensman series, the series begins with Triplanetary, beginning two billion years before the present time and continuing into the near future. The universe has no life-forms aside from the ancient Arisians, the peaceful Arisians have foregone physical skills in order to develop contemplative mental power. The Eddorians, a dictatorial, power-hungry race, come into our universe from an alien space-time continuum after observing that our galaxy and this will result in the formation of billions of planets and the development of life upon some of them. Dominance over these life forms would offer the Eddorians an opportunity to satisfy their lust for power and they see the many races in the universe, with which the Arisians were intending to build a peaceful civilization, as fodder for their power-drive. The Arisians detect the Eddorians invasion of our universe and realize that they are too evenly matched to destroy the other. It adds a short novel which is transitional to the novel First Lensman. The two lines do not commingle until the Arisian breeding plan brings them together, the second book, First Lensman, concerns the early formation of the Galactic Patrol and the first Lens, given to First Lensman Virgil Samms of Tellus. Samms and Roderick Kinnison are members of the two breeding lines and they are both leaders, intelligent, forceful, and capable. The Arisians make it known that if Samms, the head of the Triplanetary Service, visits the Arisian planetary system he will be given the tool he needs to build the Galactic Patrol. The Arisians further promise him that no entity unworthy of the Lens will ever be permitted to wear it, the Lens gives its wearer a variety of mental capabilities, including those needed to enforce the law on alien planets, and to bridge the communication gap between different life-forms. It can provide mind-reading and telepathic abilities and it cannot be worn by anyone other than its owner, will kill any other wearer, and even a brief touch is extremely painful. Their opponents are discovered to be a civilization based on dominance hierarchies. The series contains some of the space battles ever written. Entire worlds are almost casually destroyed, huge fleets of spaceships fight bloody wars of attrition. Alien races of two galaxies sort themselves into the allied, Lens-bearing adherents of Civilization and the enemy Boskone, centuries pass, and eventually the final generations of the breeding program are born

37.
E. E. Smith
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Edward Elmer Smith was an American food engineer and an early science-fiction author, best known for the Lensman and Skylark series. He is sometimes called the father of space opera, Edward Elmer Smith was born in Sheboygan, Wisconsin on May 2,1890, to Fred Jay Smith and Caroline Mills Smith, both staunch Presbyterians of British ancestry. His mother was a born in Michigan in February 1855, his father was a sailor. They moved to Spokane, Washington, the winter after Edward Elmer was born, in 1902, the family moved to Seneaquoteen, near the Pend Oreille River, in Kootenai County, Idaho. He had four siblings, Rachel M. born September 1882, Daniel M. born January 1884, Mary Elizabeth born February 1886, and Walter E. born July 1891 in Washington. In 1910, Fred and Caroline Smith and their son Walter were living in the Markham Precinct of Bonner County, Idaho, Smith worked primarily as a manual laborer until he injured his wrist, at the age of 19, while escaping from a fire. He attended the University of Idaho and he entered its prep school in 1907, and graduated with two degrees in chemical engineering in 1914. He was president of the Chemistry Club, the Chess Club, and the Mandolin and Guitar Club, whether the two were related is not known. On October 5,1915, in Boise, Idaho he married Jeanne Craig MacDougall, Jeanne MacDougall was born in Glasgow, Scotland, her parents were Donald Scott MacDougall, a violinist, and Jessica Craig MacLean. Her father had moved to Boise when the children were young, jeannes mother, who remarried businessman and retired politician John F. Kessler in 1914 worked at, and later owned, a boarding house on Ridenbaugh Street. The Smiths had three children, Roderick N. born June 3,1918, in the District of Columbia, was employed as an engineer at Lockheed Aircraft. Verna Jean, born August 25,1920, in Michigan, was his literary executor until her death in 1994, Robert A. Heinlein in part dedicated his 1982 novel Friday to Verna. Clarissa M. was born December 13,1921, in Michigan, after college, Smith was a junior chemist for the National Bureau of Standards in Washington, DC, developing standards for butter and for oysters. He may have served as a lieutenant in the U. S. Army during World War I, but details are unknown. His draft card, partly illegible, seems to show that Smith requested exemption from service, based on his wifes dependence. One evening in 1915, the Smiths were visiting a classmate from the University of Idaho, Dr. Carl Garby. He lived nearby in the Seaton Place Apartments with his wife, a long discussion about journeys into outer space ensued, and it was suggested that Smith should write down his ideas and speculations as a story about interstellar travel. Although he was interested, Smith believed that thought that some romantic elements would be required

Plaque in Building 6 honoring George Eastman, founder of Eastman Kodak, who was revealed as the anonymous "Mr. Smith" who helped maintain MIT's independence

The MIT Media Lab houses researchers developing novel uses of computer technology and shown here is the 1982 building, designed by I.M. Pei, with an extension (right of photo) designed by Fumihiko Maki opened in March 2010

1852 Map of Boston area showing Cambridge and regional rail lines and highlighting the course of the Middlesex Canal. Cambridge is toward the bottom of the map and outlined in yellow, and should not be confused with the pink-outlined and partially cropped "West Cambridge", now Arlington.

The PDP-1 (Programmed Data Processor-1) is the first computer in Digital Equipment Corporation's PDP series and was …

PDP-1 at the Computer History Museum with Steve Russell, creator of Spacewar!. The large cabinet houses the processor itself. The main control panel is just above the desk, the paper tape reader is above it (metallic), and the output of the Teletype model BRPE paper tape punch above that (vertical slot). A storage tray for eight fanfold paper tapes is attached to the top panel. At the left is the IBM Model Btypewriter modified by Soroban, and the Type 30 CRT display is to the far right.

A gravity well or gravitational well is a conceptual model of the gravitational field surrounding a body in space – the …

Plot of a two-dimensional slice of the gravitational potential in and around a uniformly dense, spherically symmetric body.

A type of embedding diagram that depicts general relativity's curvature of space. Although analogous, this does not depict the Sun's gravity well.

This image shows the four trajectory categories with the gravitational potential well (gravity well) of the central mass's field of potential energy shown in black and the height of the kinetic energy of the moving body shown in red extending above that, correlating to changes in speed as distance changes according to Kepler's laws.

This image shows how the gravitational force vector field is inter-related with the gravity well. This shows how it is only a 2‑dimensional slice of the gravity field that is represented in the gravity well. The z axis is no longer a spatial dimension, but now represents energy.

In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the …

Image: Cassini's speed related to Sun

The trajectories that enabled NASA's twin Voyager spacecraft to tour the four giant planets and achieve velocity to escape the Solar System.

Two-dimensional schematic of gravitational slingshot. The arrows show the direction in which the spacecraft is traveling before and after the encounter. The length of the arrows shows the spacecraft's speed.

Tic-tac-toe (also known as noughts and crosses or Xs and Os) is a paper-and-pencil game for two players, X and O, who …

Game of Tic-tac-toe, won by X

Optimal strategy for player X. In each grid, the shaded red X denotes the optimal move, and the location of O's next move gives the next subgrid to examine. Note that only two sequences of moves by O (both starting with center, top-right, left-mid) lead to a draw, with the remaining sequences leading to wins from X.

Optimal strategy for player O. Player O can always force a win or draw by taking center. If it is taken by X, then O must take a corner